1. Field of the Invention
The present invention relates to a hybrid material comprising an organic and an inorganic component, which is suitable for use in a special member requiring superior properties concerning heat-resistance, rigidity, resistance against solvents, and the like. The present invention also relates to a process for producing the same, and to a method for controlling the quantity of the inorganic and the organic components in the hybrid material.
2. Description of the Related Art
Hybrid materials comprising an inorganic component such as a clay mineral in combination with an organic component such as polyamide have been heretofore proposed. Hybrid materials of this type are of high practical value, because they exhibit both of the characteristics inherent in the inorganic and the organic components.
More specifically, a hybrid material comprising a layered inorganic material such as layered clay mineral and an organic material is used as a catalyst for polymerization, etc. (reference can be made to, for example, JP-A-Sho51-109998, JP-A-Sho62-72723, JP-A-Sho62-64827, JP-A-Hei5-306370, and JP-A-Hei5-32406; the term "JP-A-" as referred herein signifies "an unexamined published Japanese patent application"). In the methods proposed in the foregoing JP-A-Sho51-109998, JP-A-Sho62-72723, and JP-A-Sho62-64827, a layered clay mineral is subjected to ion-exchange treatment to obtain a layered clay mineral rendered organic by replacing the interlayer cation with an ion of an amino acid, etc. The ion-exchanged layered clay mineral thus obtained is used thereafter as a starting material for producing, for example, a polymerization catalyst, a composite, etc. The methods disclosed in JP-A-Hei5-306370 and JP-A-Hei5-32406 provide a polymerization catalyst, a composite, etc., in a manner similar to that disclosed above, except for using a zirconium phosphate type layered substance in the place of the aforementioned layered clay mineral.
For instance, JP-A-Hei5-306370 proposes a process for producing a hybrid material comprising an organic material and an inorganic material as follows.
An .alpha.- or a .gamma.-zirconium phosphate is dispersed and suspended in water, and after adding 12-aminododecanoic acid therein, the resulting suspension is stirred for a duration of from 2 to 6 hours. The resulting suspension is allowed to stand still at room temperature for a duration of several days, and a zirconium phosphate 12-aminododecanoic acid derivative is obtained by filtration, rinsing, and drying the suspension thereafter. The product thus obtained is mixed with .epsilon.-caprolactam and aminohexanoic acid, and is charged into a glass polymerization tube. After purging the gas inside the reaction tube with nitrogen, polymerization was effected by maintaining the tube at 100.degree. C. for a duration of 90 minutes, then at 250.degree. C. for 2 hours under atmospheric pressure, and finally at 250.degree. C. for 5 hours under reduced pressure. A hybrid material of zirconium phosphate and polyamide is obtained in this manner.
However, a hybrid material of an organic material and an inorganic material obtained heretofore still have problems yet to be solved. In a layered clay mineral with exchanged organic cations or a layered zirconium phosphate with an exchanged organic derivative, the layered inorganic material is bonded to an organic molecule by ionic bond. However, a substance formed by ionic bond readily undergoes an ion exchange reaction with an externally supplied ion. Accordingly, a readily exchangeable substance such as an amino acid, a diamine, and a dicarboxylic acid has been excluded from the organic constituent of the hybrid material. More specifically, for example, if an organic compound such as 6-amino-caproic acid, etc., which is capable of producing 6-nylon similar to .epsilon.-caprolactam is used, 6-amino-caproic acid and the like may be readily substituted for the previously bonded cation. In such a case, the material cannot be obtained as designed. Considering a case of a nylon produced by condensation of a diamine (NH--R--NH) with a dicarboxylic acid (COOH--R--COOH), e.g., 6,6-nylon, diamine is substituted for the previously bonded cation during the synthesis. This sometimes hinders the progress of interlayer polymerization of nylon completely, or sometimes allows the reaction progress only partly to generate a function of nylon in the interlayer. Thus, the composite thus obtained may result with little improvement in mechanical characteristics concerning elastic modulus, strength, elongation, etc., or in barrier function against gas permeation. Moreover, the resulting composite may suffer embrittlement.
Thus, it is difficult to obtain a hybrid material with the desired effect in case a polymer which uses an ionic substance during the synthesis thereof is employed. Undesirable polymers include 4,6-nylon, 6,6-nylon, 6,10-nylon, and 6,12-nylon, in which a synthesized nylon salt is subjected to polycondensation reaction, because ions previously introduced to a layered inorganic material by ion exchanging can be easily exchanged by an externally provided ion. Polyolefins such as polypropylene are also unsuitable, because metallic salts and the like are used for the polymerization catalyst. In this case, ion exchange proceeds during mixing or heating for polymerization. This hinders the formation of a composite material comprising separate and dispersed unit layers (layered structure).
Furthermore, in case of synthesizing a compound having a catalytic function by adding another inorganic ion, etc., to a layered inorganic material already rendered organic, the desired compound cannot be synthesized from a hybrid material having an ionic bond because of the ion exchange reaction. Exchange adsorption of an element or a molecule occurs depending on the difference of ionization tendency. Thus, when two types or more of organic ions were to be dispersed in the interlayer of an inorganic material, selective adsorption occurs to a certain type of ion. It can be understood therefrom that it is impossible to control the quantity of the organic ions bonded to the polymer or the quantity ratio of the organic and the inorganic materials bonded to the layer.
In case of rendering a layered inorganic material organic by an ion exchange treatment, a relatively large molecule must be intercalated between the layers by forcing it against the bonding force of the layers. If the layered inorganic material is a clay mineral, water can be used to facilitate the intercalation by expanding therewith the spacing between the layers. The same mechanism is believed to work on other types of layered substances. However, because layered inorganic materials have interlayer hydrogen bonds at a higher density than a clay mineral has, it is assumed rather difficult for the layered inorganic materials to incorporate a water molecule between the layers. Thus, in general, a reaction for a long duration of time is required in case of introducing organic ions to a layered inorganic material completely. Furthermore, even if the reaction for rendering the inorganic material organic should proceed to such an extent as to attain an average basal spacing in a range of from 15 to 30 .ANG., even a few bondings between layers may prevent the material from swelling by intercalating polymer. In such a case, the expected effects cannot be obtained.
To obtain a material having a novel function by controlling the alignment of the organic molecules therein, or to intensify the function as a barrier for gas permeation by dispersing large lamella crystals, the layered inorganic material must be previously developed into coarse and perfect crystals by crystal growth. Concerning a case of growing crystals of a clay mineral, for instance, a smectite group mineral readily forms an intercalated compound, but it changes into a large vermiculite crystal which takes a long time for intercalation, and then to a mica mineral which rarely takes up other interlayer cations. In case of other layered inorganic compounds such as zirconium phosphate, it is difficult to render the compounds organic because the compound tends to adsorb less organic ions as the crystals grow large. Moreover, it becomes more difficult to polymerize the organic ions with increasing the size of crystals. Accordingly, so long as the inorganic substance is rendered organic based on ion adsorption, it is found difficult to control the size and the perfection of a crystal.
On the other hand, the dispersibility in the later step of polymerization can be increased by reducing the size of the crystals. However, there is a limit in controlling the crystal size. That is, in case of a naturally occurring mineral such as a clay mineral, the size and the like of the crystals depend on the raw material. It is difficult to obtain crystals with a smaller or specific size, if any, among naturally occurring minerals. In case of synthesizing artificially a clay mineral or other types of layered inorganic materials, it is necessary to perform some crystallization by hydrothermal reaction or by gelation at room temperature followed by a treatment such as heating or hydrothermal reaction. Further crystallization treatment is necessary after simple gelation at room temperature is performed, because most of the products are obtained at amorphous states by the gelation. The desired material cannot be obtained unless crystallization reaction is effected to a certain extent.
Referring to a schematically drawn structure given in FIG. 2, a layered clay mineral in general comprises an octahedral sheet consisting of a plurality of octahedra bonded with each other and each containing aluminum or magnesium in the octahedral site, being 6-fold coordinated with oxygen or hydroxyl groups. A tetrahedral sheet consisting of SiO.sub.4 tetrahedra is bonded by plane to plane with the octahedral sheet to provide a layered structure. In case of bonding an organic portion directly with the inorganic structural unit above, an --O--Si--C--R (where R represents an organic portion) bond must be incorporated by once cutting the Si--O--Si bond of the tetrahedral sheet. Although this is not impossible, lattice defects must be inevitably introduced into the crystals.
Referring to the schematically drawn zirconium phosphate structure in FIG. 3, reversely to the case of a clay mineral, the apices of the tetrahedral sheet are pointed in the direction opposite to the octahedral sheet. Exchangeable cations such as H.sup.+ are bonded to the apical oxygen. In a common zirconium phosphate, organic cations are bonded by ionic bonds at the cationic sites. In such a structure, an --Si--C--R bond as illustrated in FIG. 1 can be introduced by substituting carbon for the apical oxygen located at the outer side of the tetrahedral sheet without inducing any defects in the crystal structure.
Organic derivatives of zirconium phosphates containing organic portion (R) directly bonded to an inorganic layer of this type are described in, for example, G. Alberti and U. Costautino, in Chap. 5 of Intercalation Chemistry (Edited by M. S. Whittingham and A. J. Jacobson), Academic Press (1982). However, no information is available on the synthetic process for obtaining a composite of the substance and the polymer, the characteristics of a composite, and the means for realizing the effect of the composite as a polymerization catalyst.
As described in the foregoing, hybrid materials having been proposed in the prior arts comprise an organic material and an inorganic material bonded with each other by an ionic bond. Accordingly, only limited types of organic materials are usable for the composite. In particular, industrially useful 6,6-nylon and polyolefins cannot be used in a hybrid material. Furthermore, because large layered inorganic materials are not available, the control of gas permeability and the like is still limited in case of using the hybrid materials known to the present.
In U.S. Pat. No. 4,298,723 is proposed a hybrid material comprising an organic compound bonded by covalent bond with an inorganic compound. The hybrid material disclosed therein comprises a layered structure comprising an octahedral sheet consisting of octahedra bonded with each other in a sheet-like manner and a tetrahedral sheet consisting of tetrahedra bonded with each other in a sheet-like structure, and an organic compound bonded to the layered structure. The octahedra comprises oxygen arranged in a 6-fold coordination with respect to a tetravalent element such as zirconium in the octahedral site, and the tetrahedra comprises oxygen arranged in a 4-fold coordination with respect to a pentavalent element such as phosphorus located at the tetrahedral site. The organic compound is bonded by covalent bond to the tetrahedral metal of the layered structure.
The only organic compound which is included in the hybrid material of the aforementioned prior art is an acrylic acid. The composite is used specifically as an adsorbent to adsorb particular components from a medium, an additive (filler) for a polymer composition, or a solid lubricant, etc. However, the superior characteristics inherent in an organic material, such as high tensile strength, are not still expected because the composite has a basal spacing as short as 4.2 nm or even less. Furthermore, the composite has poor formability.